scholarly journals Flicker fusion thresholds as a clinical identifier of a magnocellular-deficit dyslexic subgroup

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jessica L. Peters ◽  
Edith L. Bavin ◽  
Alyse Brown ◽  
David P. Crewther ◽  
Sheila G. Crewther
Keyword(s):  
Visual Processing ◽  
Temporal Frequency ◽  
Reading Rate ◽  
Naming Speed ◽  
Temporal Contrast ◽  
High Temporal Frequency ◽  
Appropriate Treatment ◽  
Dyslexic Group ◽  
Lower Ability ◽  
Flicker Fusion

AbstractThe magnocellular-dorsal system is well isolated by high temporal frequency. However, temporal processing thresholds have seldom been explored in developmental dyslexia nor its subtypes. Hence, performances on two, four-alternative forced-choice achromatic flicker fusion threshold tasks modulated at low (5%) and high (75%) temporal contrast were compared in dyslexic and neurotypical children individually matched for age and intelligence (8–12 years, n = 54 per group). As expected, the higher modulation resulted in higher flicker fusion thresholds in both groups. Compared to neurotypicals, the dyslexic group displayed significantly lower ability to detect flicker at high temporal frequencies, both at low and high temporal contrast. Yet, discriminant analysis did not adequately distinguish the dyslexics from neurotypicals, on the basis of flicker thresholds alone. Rather, two distinct dyslexic subgroups were identified by cluster analysis – one characterised by significantly lower temporal frequency thresholds than neurotypicals (referred to as ‘Magnocellular-Deficit’ dyslexics; 53.7%), while the other group (‘Magnocellular-Typical’ dyslexics; 46.3%) had comparable thresholds to neurotypicals. The two dyslexic subgroups were not differentially associated with phonological or naming speed subtypes and showed comparable mean reading rate impairments. However, correlations between low modulation flicker fusion threshold and reading rate for the two subgroups were significantly different (p = .0009). Flicker fusion threshold performances also showed strong classification accuracy (79.3%) in dissociating the Magnocellular-Deficit dyslexics and neurotypicals. We propose that temporal visual processing impairments characterize a previously unidentified subgroup of dyslexia and suggest that measurement of flicker fusion thresholds could be used clinically to assist early diagnosis and appropriate treatment recommendations for dyslexia.

scholarly journals Critical Flicker Fusion Frequency: A Narrative Review

Medicina ◽  
2021 ◽  
Vol 57 (10) ◽  
pp. 1096
Author(s):  
Natalia D. Mankowska ◽  
Anna B. Marcinkowska ◽  
Monika Waskow ◽  
Rita I. Sharma ◽  
Jacek Kot ◽  
...  
Keyword(s):  
Visual Processing ◽  
Current Knowledge ◽  
Minimal Hepatic Encephalopathy ◽  
Future Research ◽  
Critical Flicker Fusion ◽  
Flicker Fusion Frequency ◽  
Fusion Frequency ◽  
Critical Flicker Fusion Frequency ◽  
Model Studies ◽  
Flicker Fusion

This review presents the current knowledge of the usage of critical flicker fusion frequency (CFF) in human and animal model studies. CFF has a wide application in different fields, especially as an indicator of cortical arousal and visual processing. In medicine, CFF may be helpful for diagnostic purposes, for example in epilepsy or minimal hepatic encephalopathy. Given the environmental studies and a limited number of other methods, it is applicable in diving and hyperbaric medicine. Current research also shows the relationship between CFF and other electrophysiological methods, such as electroencephalography. The human eye can detect flicker at 50–90 Hz but reports are showing the possibility to distinguish between steady and modulated light up to 500 Hz. Future research with the use of CFF is needed to better understand its utility and application.

Processing of Natural Time Series of Intensities in the Early Visual System of the Blowfly

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 24-24 ◽  
Author(s):  
J H van Hateren
Keyword(s):  
Time Series ◽  
Visual System ◽  
Visual Processing ◽  
Time Course ◽  
Temporal Frequency ◽  
Power Spectra ◽  
Calliphora Vicina ◽  
Intensity Measurements ◽  
Natural Time ◽  
Early Visual System

The first steps of processing in the visual system of the blowfly are well suited for studying the relationship between the properties of the environment and the function of visual processing (eg Srinivasan et al, 1982 Proceedings of the Royal Society, London B216 427; van Hateren, 1992 Journal of Comparative Physiology A171 157). Although the early visual system appears to be linear to some extent, there are also reports on functionally significant nonlinearities (Laughlin, 1981 Zeitschrift für Naturforschung36c 910). Recent theories using information theory for understanding the early visual system perform reasonably well, but not quite as well as the real visual system when confronted with natural stimuli [eg van Hateren, 1992 Nature (London)360 68]. The main problem seems to be that they lack a component that adapts with the right time course to changes in stimulus statistics (eg the local average light intensity). In order to study this problem of adaptation with a relatively simple, yet realistic, stimulus I recorded time series of natural intensities, and played them back via a high-brightness LED to the visual system of the blowfly ( Calliphora vicina). The power spectra of the intensity measurements and photoreceptor responses behave approximately as 1/ f, with f the temporal frequency, whilst those of second-order neurons (LMCs) are almost flat. The probability distributions of the responses of LMCs are almost gaussian and largely independent of the input contrast, unlike the distributions of photoreceptor responses and intensity measurements. These results suggest that LMCs are in effect executing a form of contrast normalisation in the time domain.

scholarly journals Orientation Tuning, But Not Direction Selectivity, Is Invariant to Temporal Frequency in Primary Visual Cortex

2005 ◽  
Vol 94 (2) ◽  
pp. 1336-1345 ◽  
Author(s):  
Bartlett D. Moore ◽  
Henry J. Alitto ◽  
W. Martin Usrey
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Visual Stimulus ◽  
Visual Processing ◽  
Cortical Neurons ◽  
Temporal Frequency ◽  
Direction Selectivity ◽  
Orientation Tuning ◽  
Orientation Contrast ◽  
Wide Range

The activity of neurons in primary visual cortex is influenced by the orientation, contrast, and temporal frequency of a visual stimulus. This raises the question of how these stimulus properties interact to shape neuronal responses. While past studies have shown that the bandwidth of orientation tuning is invariant to stimulus contrast, the influence of temporal frequency on orientation-tuning bandwidth is unknown. Here, we investigate the influence of temporal frequency on orientation tuning and direction selectivity in area 17 of ferret visual cortex. For both simple cells and complex cells, measures of orientation-tuning bandwidth (half-width at half-maximum response) are ∼20–25° across a wide range of temporal frequencies. Thus cortical neurons display temporal-frequency invariant orientation tuning. In contrast, direction selectivity is typically reduced, and occasionally reverses, at nonpreferred temporal frequencies. These results show that the mechanisms contributing to the generation of orientation tuning and direction selectivity are differentially affected by the temporal frequency of a visual stimulus and support the notion that stability of orientation tuning is an important aspect of visual processing.

Hazardous nature of high-temporal-frequency strobe light stimulation: neural mechanisms revealed by magnetoencephalography

Neuroscience ◽  
2010 ◽  
Vol 166 (2) ◽  
pp. 482-490 ◽  
Author(s):  
Y. Shigihara ◽  
M. Tanaka ◽  
N. Tsuyuguchi ◽  
H. Tanaka ◽  
Y. Watanabe
Keyword(s):  
Temporal Frequency ◽  
Neural Mechanisms ◽  
Light Stimulation ◽  
Strobe Light ◽  
High Temporal Frequency

scholarly journals A Development Strategy for SHM Applications

2021 ◽  
pp. 1-17
Author(s):  
Peter Cawley
Keyword(s):  
Spatial Frequency ◽  
Development Strategy ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Operating Conditions ◽  
Damage Growth ◽  
Periodic Inspection ◽  
High Temporal Frequency ◽  
Industrial Use ◽  
Signal Changes

Abstract Permanently installed SHM systems are now a viable alternative to traditional periodic inspection (NDT). However, their industrial use is limited and this paper reviews the steps required in developing practical SHM systems. The transducers used in SHM are fixed in location, whereas in NDT they are generally scanned. The aim is to reach similar performance with high temporal frequency, low spatial frequency SHM data to that achievable with conventional high spatial frequency, low temporal frequency NDT inspections. It is shown that this can be done via change tracking algorithms such as the Generalized Likelihood Ratio (GLR) but this depends on the input data being normally distributed, which can only be achieved if signal changes due to variations in the operating conditions are satisfactorily compensated; there has been much recent progress on this topic and this is reviewed. Since SHM systems can generate large volumes of data, it is essential to convert the data to actionable information, and this step must be addressed in SHM system design. It is also essential to validate the performance of installed SHM systems, and a methodology analogous to the model assisted POD (MAPOD) scheme used in NDT has been proposed. This uses measurements obtained from the SHM system installed on a typical undamaged structure to capture signal changes due to environmental and other effects, and to superpose the signal due to damage growth obtained from finite element predictions. There is a substantial research agenda to support the wider adoption of SHM and this is discussed.

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